Official OS X Mountain Lion.app Installer from the Mac App Store.
Both versions 10.8.4 AND 10.8.5 full installers included (zipped).
the zip archive and you will get the app Installer. A bootable ISO or
bootable USB can be made directly from the InstallESD.dmg disk image found under Contents/SharedSupport/. Instructions on how to do
that are on the Internet/Youtube.